<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .t {
            width: 800px;
            margin: auto;
            border: 1px solid #000;
            line-height: 40px;

            /* 边框合并   此属性只有表格可以使用 */
            border-collapse: collapse;

            /* 固定宽高  防止宽高被内容撑开 */
            table-layout: fixed;
        }

        /* td,
        th {
            height: 40px;
            border-bottom: 1px solid #000;
        } */

        th,
        td {
            border: 1px solid #000;
            height: 40px;
            width: 20%;
        }
    </style>
</head>

<body>

    <table class="t" cellspacing="0">
        <tr>
            <th>11111111111111111111111111111111</th>
            <th>2</th>
            <th>3</th>
            <th>4</th>
            <th>5</th>
        </tr>

        <tr>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
        </tr>
        <tr>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
        </tr>
        <tr>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
        </tr>
        <tr>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
            <td></td>
        </tr>
    </table>

</body>

</html>